Pneumatic tire and tire wheel assembly

ABSTRACT

The reduction of noise in the rotation of the tire and the improvement of resistance to hydroplaning are established and also the resistance to uneven wear is improved, in which four circumferential main grooves  2 - 5  are formed asymmetrically, and a sum of groove volume in a circumferential direction in lateral grooves formed in a shoulder land part row  7  as a portion of an axially inner side per unit width is made smaller than a sum of groove volume in the circumferential direction in lateral grooves  11  formed in a shoulder land part row  9  as a portion of an axially outer side and a land part row  6  in a central region is rendered into a rib, and slant grooves  13  extending at an average inclination angle of not less than 45° with respect to a widthwise direction of the tread are arranged in a second inner land part row  8  located at a side of an equatorial line adjacent to the shoulder land part row  7  at the axially inner side and these slant grooves  13  are opened to the circumferential main groove located adjacent to the second inner land part row  8  of the axially inner side.

TECHNICAL FIELD

This invention relates to a pneumatic tire simultaneously establishing anoise reduction during the rotation of the tire and a resistance tohydroplaning and improving a resistance to uneven wear as well as atire-wheel assembly.

BACKGROUND ART

As a conventional technique improving wet performances of a tire andcontrolling an uneven wear and a tire noise, there is one disclosed inJP-A-10-217719.

According to this technique, when a tire tread is virtually divided intoan outer region directing to an outer side of a vehicle and an innerregion directing to an inner side of the vehicle with respect to anequator of the tire, one longitudinal outer main groove linearlyextending in a circumferential direction of the tire is arranged in theouter region and first and second longitudinal inner main grooveslinearly extending in the circumferential direction of the tire arearranged in the inner region, and these longitudinal main grooves areasymmetric with respect to the equator of the tire, and outer slantgrooves inclined at an angle of 45-70° with respect to thecircumferential direction are arranged at given intervals in an outershoulder portion between the longitudinal main groove in the outerregion and a ground contact end of the outer region and inner slantgrooves inclined at an angle of 60-80° with respect to thecircumferential direction and opposed to the outer slant grooves arearranged at given intervals in an inner shoulder portion between thesecond longitudinal inner main groove and a ground contact end of theinner region, and central slant grooves inclined at an angle of 20-45°with respect to the circumferential direction and in the same directionas the outer slant groove are arranged at given intervals in a crownportion between the longitudinal outer main groove and the secondlongitudinal inner main groove. Thus, the wet performances are enhancedand noise through columnar resonance can be reduced under the action ofthe one longitudinal outer main groove and the two longitudinal innermain grooves, and also premature wear at the outer region of the tiremounted onto the vehicle can be controlled.

As the other conventional technique, as disclosed in JP-A-2000-238510,there is a pneumatic tire for a vehicle wherein a tread pattern isasymmetrically formed with respect to a circumferential direction of atread surface and comprises outer and inner regions having shoulderblock rows and a central region defining both sides by circumferentialgrooves belonging to the above regions, and lateral grooves arecontinued from the shoulder block row of the inner region to the centralregion, and a width of the central region in the tread pattern is 25-35%of a tread width, and alternating lateral grooves among the lateralgrooves extending from the shoulder block row of the inner region atmaximum are continued in the central region as a groove substantiallycrossing at least the central region and these grooves are inclined atan angle of 30° at maximum with respect to the equatorial line over atleast ⅓ of a length of the central region. In this technique, thedrainage property is improved by making the wearing of the patternuniform as far as possible and a good influence is given to the noiseduring the rotation.

In these tires, however, the sufficient consideration is not made on theresistance to hydroplaning at a road surface having a water depth deeperthan a wet road surface. Further, since they are designed withoutconsidering the application of a camber angle to the tire when the tireis mounted onto a vehicle, the noise reduction during the rotation ofthe tire and the resistance to hydroplaning can not be well establishedin the actual running of the vehicle mounted with such tires, and alsothere is a problem that uneven wear is created in an inner portion ofthe tire mounted on the vehicle.

The invention is to solve the above problems inherent to theconventional techniques and to provide a pneumatic tire in which thenoise reduction during the rotation of the tire and the improvement ofthe resistance to hydroplaning are simultaneously established in ahigher dimensionality and also the resistance to uneven wear iseffectively improved.

DISCLOSURE OF THE INVENTION

In the designing of the asymmetric tread pattern, it has widely andgenerally been conducted from the old time that the negative ratio ismade small in an axially outer portion of the tire mounted on thevehicle by emphasizing the running performances of the tire on a dryroad surface, while the negative ratio is made large in an axially innerside portion of the tire mounted on the vehicle for ensuring the wetperformances.

In the tire having a tread pattern of such a construction, however, whena negative camber is particularly applied to the tire in use, there areproblems that the wearing of the tread in the axially inner side portionbecomes violent and also the steering stability at a state near to astraight running state lowers and further the resistance to hydroplaningis not improved.

Considering the tread wearing among them, a ground contact length of ashoulder portion at the axially inner side is longer than that of ashoulder portion at an axially outer side in the application of thenegative camber, so that if a slight slip angle such as a toe angle orthe like is applied to the tire, the inner shoulder portion bears toomuch a lateral force against a lateral slippage. Also, a longitudinaldeflection at the axially inner side becomes larger than a longitudinaldeflection at the axially outer side in the application of the negativecamber and such a large longitudinal deflection brings about thereduction of the rotating radius of the tire. For this end, asmall-diameter side portion of a ground contact face of the tread isrelatively subjected to a force in a braking direction by draggingthrough a large-diameter side portion thereof. They result in a cause ofpremature wear of the tread at the axially inner side, or uneven wear ofthe tread.

In this case, the bearing of force becomes generally large in a regionnear to the ground contact end and a nucleus for the uneven wear is aptto be easily created in this region, and the thus created uneven weargradually progresses toward a side of an equatorial line of the tire.

On the other hand, in order to improve the steering stability at arunning state near to a straight running state such as the running on anexpressway or the like, it is effective to provide a tread pattern sothat the rigidity in the widthwise direction of the tread is made largein each of a central portion of the tread increasing particularly a belttension under the filling of an internal pressure and a portion of thetread particularly prolonging a ground contact length to be largelyaffected by a rigidity of the tread pattern. In case of giving thenegative camber to the tire, a portion having a longest ground contactlength is displaced somewhat from the tread central portion toward theaxially inner side. In the latter case, it is preferable to form a treadpattern having a high rigidity in the widthwise direction extendedbetween the tread central portion and the longest ground contact lengthportion, e.g. a rib. By arranging a circumferential main groove to therib at the axially inner side or in the both sides of the rib is formeda drainage flow line substantially directing to the circumferentialdirection of the tread, whereby water on the road surface can be drainedefficiently to advantageously prevent the occurrence of hydroplaningphenomenon.

As a result of analysis through a finite element method for improvingthe resistance to hydroplaning, it is clear that a most water-reservingportion or a portion having a low drainage function is existent in aside having a long ground contact length rather than the tread centralportion due to the fact that the longest ground contact length portionis displaced somewhat from the tread central portion toward the axiallyinner side in the application of the negative camber. Therefore, it ispossible to improve the resistance to hydroplaning by arranging thecircumferential main groove in such a portion to enhance the drainageperformance.

Also, it is preferable that the drainage is conducted toward the outerside in both outer regions located outward from the circumferential maingrooves. In this case, the drainage groove is preferable to be extendedalong a direction of water flow line. Since the flow line in thevicinity of the shoulder portion corresponding to the portion of theaxially inner side directs toward the widthwise outer side at an angleof not less than 45° with respect to the widthwise direction of thetread, it is preferable that the drainage groove is formed in such aflow line direction and opened to the circumferential groove at leastlocated at the widthwise outer side for more further improving theresistance to hydroplaning.

In the pneumatic tire according to the invention, therefore, three ormore circumferential main grooves asymmetrically positioned with respectto an equatorial line of the tire and extending linearly andcontinuously in the circumferential direction of the tread are formed ina ground contact face of the tread and one or more land part rows areformed in each of the resulting central region and both side regions, inwhich a sum of groove volume in a circumferential direction in lateralgrooves formed in a shoulder land part row corresponding to an axiallyinner side position of the tire mounted on a vehicle per unit width ismade smaller than a sum of groove volume in the circumferentialdirection in lateral grooves formed in a shoulder land part rowcorresponding to an axially outer side position of the tire mounted onthe vehicle, and the land part row in the central region including theequatorial line of the tire or located nearest to the equatorial line isrendered into a rib, and a plurality of slant grooves extending at anaverage inclination angle of not less than 45° with respect to awidthwise direction of the tread are arranged in a second inner landpart row located at a side of the equatorial line adjacent to a shoulderland part row in the axially inner side and these slant grooves areopened to the circumferential main groove at least located adjacent tothe second inner land part row of the axially inner side.

The term “circumferential main groove” used herein means a groove havinga groove width corresponding to not less than 2.5% of a tread width.

Moreover, the term “tread width” used herein means a ground contactwidth when the tire is mounted onto an approved rim and filled with adefined air pressure and loaded under a mass corresponding to a maximumload capacity. In this case, the approved rim means a rim defined in thefollowing standard, and the maximum load capacity means a maximum massapplicable to the tire in the following standard, and the defined airpressure means an air pressure defined in correspondence with themaximum load capacity in the following standard.

The standard is one decided by an industrial standard effective in anarea producing tires or using them, for example, “YEAR BOOK of THE TIREAND RIM ASSOCIATION INC.” in USA, “STANDARDS MANUAL of The European Tyreand Rim Technical Organization” in Europe, and “JATMA YEAR BOOK” of TheJapan Automobile Tire Manufacturers Association Inc. in Japan.

According to this tire, the sum of groove volume in the circumferentialdirection in the lateral grooves formed in the shoulder land part rowcorresponding to the axially inner side is made smaller than the sum ofgroove volume in the circumferential direction in the lateral groovesformed in the shoulder land part row corresponding to the axially outerside to effectively deal with the aforementioned causes of creating theuneven wear in case of applying the negative camber to the tire in use,whereby the balance of braking force and traction force between theaxially inner side and the axially outer side can be enhanced toeffectively improve the resistance to uneven wear.

That is, the uneven wear resulted from the fact that the inner shoulderland part row bears a larger lateral force, in the application of thenegative camber, toe angle or the like can be done by making the ratioof the grooves occupied in this shoulder land part row small to enhancethe rigidity of this land part row. Also, the uneven wear resulted fromthe fact that the rotating radius at the axially inner side is madesmall by the longitudinal deflection of the tire can be done bydeforming the shoulder land part row in a direction of reducing thelateral groove width within the ground contact face to suppress thecontraction of the rotating radius based on the fact that the totalvolume of the lateral grooves in such a land part row is made small.

Further, when the negative camber is applied to the tire, the groundcontact form of the tire is determined by an alignment in the vehicle,an internal pressure of the tire, a mass loaded and the like, and theland part row in the central region as a portion having a longest groundcontact length is rendered into a rib to enhance the rigidity in thewidthwise direction of the tread, whereby the steering stability can beeffectively improved against the application of a relatively small slipangle to the tire under a running state near to the straight runningstate.

When the negative camber is applied to such a tire, the water pressuredistribution at the axially inner side is made higher than that at theaxially outer side due to the fact that water on the road surface iseasily reserved in the circumferential main groove located inward fromthe equatorial line of the tire and extending nearest to the equatorialline and the second land part row located adjacent to such acircumferential main groove at the axially inner side.

In order to improve this problem, slant grooves guiding water on theroad surface in a direction separating from the tread center arearranged in the second inner land part row and the extending directionof the slant grooves is made not less than 45° with respect to thewidthwise direction of the tread in conformity with the inclination ofthe drainage flow line at the axially inner side, whereby the smoothnessand rapidness of the drainage are guaranteed.

When the rib of the central land part row having a high rigidity in thewidthwise direction as mentioned above is arranged so as to extendbetween the tread central portion and the portion having a longestground contact length, the belt tension in the second inner land partrow is smaller than that in the tread central portion and also theground contact length in the inner land part row shorter than that inthe rib and the ratio of the second inner land part row contributing tothe steering stability is not so large, so that even if the extendingangle of the slant grooves in the second inner land part row is made notless than 45° as mentioned above, it does not exert a large influence onthe steering stability. Also, the ratio of the grooves in the shoulderland part row at the axially inner side is made smaller than that in theshoulder land part row at the axially outer side as previouslymentioned, so that even if the extending angle of the slant groovebecomes large, the resistance to uneven wear is not so damaged againstthe bearing of the inner shoulder land part row to force in the groundcontact face.

Furthermore, in connection with the resistance to hydroplaning, thedrainage flow line in the shoulder land part row at the portion of theaxially outer side extends substantially in the widthwise direction ofthe tread, so that it is preferable to extend the lateral grooves in theshoulder land part row as a portion of the axially outer side toward theflow line direction. On the other hand, in the shoulder land part row ata portion of the axially inner side, the ground contact form is roundedto effectively obstruct the penetration of water on the road surfaceinto the inner side of the ground contact face of the tread under anaction inherent to a ground contact profile of the tread, so that thereis caused no lowering of the resistance to hydroplaning withoutarranging the lateral grooves in this row.

Preferably, four or more circumferential main grooves are arranged, anda plurality of lateral grooves are arranged in a second outer land partrow adjacent to an equatorial line side of a shoulder land part row atthe portion of the axially outer side, wherein one end of each lateralgroove is opened to the circumferential main groove and the other endthereof is terminated in the land part row.

In order to improve the resistance to hydroplaning, it is preferable tomake the number of the lateral grooves or the like large. In this case,however, it can not be avoided to increase noise due to the butting ofthe edge of the lateral groove with the road surface during the runningof the tire under loading. Also, if the adjoining circumferential maingrooves are communicated with each other through the lateral grooves, alarge columnar resonance sound common to both the circumferential maingrooves is created.

In the invention, therefore, one end of the lateral groove is opened tothe circumferential main groove to ensure the excellent drainageperformance, while the other end is terminated in the land part row,whereby the columnar resonance frequency of each circumferential maingroove is separated to disperse peak values of the resonance sound andthe butting length of the edge of the lateral groove with the roadsurface is reduced to realize the reduction of the noise.

Also, it is preferable that a circumferential fine groove having agroove width corresponding to less than 2.5% of a tread width isarranged in the shoulder land part row being the axially inner side todivide the shoulder land part row into two parts, and an averageinclination angle of the lateral groove arranged in the shoulder landpart row being the axially outer side with respect to the widthwisedirection of the tread is made not more than 15°.

In this case, a portion of the inner shoulder land part row in thevicinity of the ground contact end easily tending to cause the unevenwear is separated from the other portion of this shoulder land part rowby the circumferential fine groove, whereby the progress of the unevenwear generated in the portion near to the ground contact end to theother portion of the shoulder land part row can be suppressedadvantageously.

As a result of the analysis on the resistance to hydroplaning, it isclear that the position of the drainage flow line directing to thecircumferential direction of the tread is displaced from the treadcentral portion toward the inner shoulder side in the application of thenegative camber as compared with the case of applying no negativecamber, while the ground contact profile is rounded at the side of shortground contact length and is effective in the drainage toward the outerside in the widthwise direction of the tread, and the extendingdirection of the drainage flow line in the outer shoulder land part rowis not more than 15° with respect to the widthwise direction of thetread. In the invention, therefore, the extending direction of thelateral groove in the outer shoulder land part row is made not more than15° with respect to the widthwise direction of the tread to enhance thedrainage efficiency and ensure the improvement of the resistance tohydroplaning.

On the other hand, the widthwise rigidity of the shoulder land part rowbeing the axially outer side of shorter ground contact length largelyaffects the steering stability in the application of a relatively largeslip angle as particularly exemplified by the running on mountain path.In this case, therefore, an average angle of the lateral groove formedin the shoulder land part row is made not more than 15° with respect tothe widthwise direction of the tread to suppress the lowering of thewidthwise rigidity of such a land part row, whereby the excellent wearresistance is provided while ensuring the high steering stability.

Preferably, the shoulder land part row as a portion of the axially innerside is divided into tow parts in the widthwise direction by a finegroove extending in the circumferential direction, and one dividedportion located at the side of tread end is a narrow-width rib, and aplurality of small holes separated from the groove are arranged in theother wide-width divided portion which may be provided with the lateralgrooves.

For example, when a load is applied to the tire at a state of giving thenegative camber angle to the tire, the ground contact length at theground contact face of the tread in the circumferential direction of thetread becomes longer in the portion of the axially inner side andshorter in the outer portion as a standard of tire posture at a camberangle of zero, and the wheel rim is approached to the road surface tomake a rotating radius small in the axially inner side increasing theground contact length and the rotating radius is made large in theaxially outer side decreasing the ground contact length, so that thereis a problem that a relative force in a braking direction is applied tothe portion of the axially inner side to cause a premature wear, forexample, at a state of straight running the vehicle. As a conventionaltechnique for suppressing such a premature wear, JP-A-2001-354010discloses that the rigidity of the shoulder land part at the axiallyinner side in the circumferential direction of the tire mounted onto thevehicle set to the negative camber is made larger than the rigidity ofthe shoulder land part at the axially outer side in the circumferentialdirection of the tire to enhance the wear resistance in the brakingdirection of the shoulder land part at the axially inner side or at theside increasing the ground contact length.

However, it has newly been found that according to only thisconstruction, when force applied to the tire from a lateral directionthereof is increased by cornering or the like, the ground contactpressure of the shoulder land part increasing the rigidity in thecircumferential direction becomes large and a nucleus for the unevenwear is easily created at this part.

On the contrary, the shoulder land part row at the axially inner side isdivided into two parts in the widthwise direction by the fine grooveextending in the circumferential direction and one narrow-width dividedpart located at the side of the tread end is acted as a wear-sacrificingportion as mentioned above, whereby the progress of the wear created atthis part toward the other wide-width divided part located at the sideof the tread center can be advantageously suppressed to protect thewide-width divided part from the premature wear.

Also, a plurality of small holes separated from the groove are formed inthe wide-width divided part to reduce shearing rigidity of such adivided part at the ground contact face in all directions, whereby thebearing of force under a high flexibility can be advantageouslydecreased to advantageously mitigate the premature wear even if thewide-width divided part is dragged into the braking direction or even ifan input of lateral force to such a part is increased.

In such a tire, when the groove width of the circumferential fine grooveformed in the shoulder land part row of the axially inner side isgradually or stepwise widened at a side of the tread surface as comparedwith the groove bottom, even if foreign matters such as pebbles and thelike on the road surface are bitten into the fine groove, thegetting-off of the foreign matter from the fine groove is facilitated,whereby it is effectively prevented to create the uneven wear resultedfrom the running of the tire at a state of biting the foreign matter inthe fine groove under loading in the other part divided by the finegroove and located at the equatorial line side of the tire.

Also, when a total volume of plural small holes formed in the wide-widthdivided part at the shoulder land part row of the axially inner side inthe circumferential direction of the tread is made larger at a side ofthe fine groove than at a side of the equatorial line of the tire, asthe bearing of lateral force becomes large near to the ground contactend, the rigidity of the wide-width divided part is reduced to receivean input of the force on a wider region, whereby the deformation can bedecreased to effectively prevent the wearing of such a divided part.Also, the high steering stability and the tread durability can beensured as compared with the case that the total volume of small holesis made large over the whole of the wide-width divided part.

In this case, the change in the total volume of small holes can berealized, for example, by changing an opening size or depth of the smallhole, by changing an arranging pitch of the small holes or the like.

On the other hand, when the tread structure including the small holeforming region for the wide-width divided part is a tread structure thatthe wide-width divided part provided with the small holes is contactedin at least a part of the small hole forming region with ground at aposture of applying a camber angle of −0.5 under an action of a loadcorresponding to 40% of a maximum load capacity, even if the loadbecomes small and the ground contact width becomes narrow in the rearwheeled tire as compared with the front wheeled tire in the braking ofFF vehicle, the effect of reducing the rigidity under the action of thesmall holes can be developed effectively.

Also, when a side face of a narrow-width rib formed by dividing theshoulder land part row of the axially inner side through thecircumferential fine groove and located at the side of the tread end isa concave curved form having a center of curvature at the outer side ofcross sectional profile line, the wearing volume of the narrow-width ribas a wear sacrificing portion can be reduced to suppress the change ofappearance to a new tire small and improve the wearing appearance.

In such a tire, it is preferable that a center line of a rib as a landpart row of a central region located nearest to the equatorial line ofthe tire is positioned toward the axially inner side with respect to theequatorial line and a plurality of widthwise fine grooves extendingobliquely with respect to the widthwise direction of the tread arearranged in such a rib.

In this case, it is preferable that the inclination angle of thewidthwise fine groove is an average angle of 5-55° and a groove widththereof is not more than 2 mm.

In order to improve the griping force and steering stability on a roadsurface in case of running on a dry road surface at a high speed or thelike, it is preferable to arrange a land part row such as a rib beinghigh in the rigidity in the widthwise direction of the tread and capableof rapidly and surely transmitting the input to a high tension portionof a belt in the tire between a tread central portion becoming largestin a tension of the belt having a so-called hoop effect to bring about ahigh rigidity of the tread and a portion being longest in the groundcontact length of the tread, or at a position extending between both theportions.

In such a rib, however, when the escape deformation of the tread rubberin the circumferential direction is not allowed, the uneven wear iscaused in this rib. In the invention, therefore, the widthwise finegrooves having a width of not more than 2 mm and an extending angle of5-55° are formed in the rib as a land part row so as to allow a properescape deformation in the circumferential direction while ensuring therigidity in the widthwise direction of the tread.

The reason why the groove width is limited to not more than 2 mm is dueto the fact that a slight groove width is enough to absorb the escapedeformation of rubber in the circumferential direction and if it exceeds2 mm, the pattern noise increases but also the lowering of the rigidityin the widthwise direction of the rib becomes large. Also, when theangle of the fine groove is less than 5°, it is not avoided to increasethe pattern noise due to the impact contact of the groove edge with theroad surface, while the upper limit of 55° is due to the fact that whenit exceeds 55°, the rigidity in the widthwise direction of the ribbecomes too low.

Preferably, the widthwise fine groove is formed so as to incline in adepth direction in form of a flat face, a curved face or the likeprovided that the fine groove is separated away from each other in agroove width direction, a circumferential direction of the tread or thelike around a middle portion of the extending direction of the finegroove. In this case, the number of the flat faces or the like inclinedin a direction of separating from each other may be three or more perone fine groove.

According to this construction, the escape deformation of rubber in thecircumferential direction is sufficiently allowed in the presence of thefine groove having a given groove width, while the fine groove ismutually interfered at the side of the groove bottom rather than theopening position in the widthwise direction of the tread, whereby thelowering of the rigidity of the land part row as a rib in the widthwisedirection can be prevented effectively.

At least a part of the plural widthwise fine grooves can be terminatedin the rib as a land part row at both ends of the extending direction,whereby the steering stability can be more improved while keeping therigidity in the widthwise direction of the rib at a high level.

That is, the allowance of the escape deformation of rubber in thecircumferential direction is particularly required at a widthwisecentral portion of the rib having no escape of rubber, so that even ifthe widthwise fine groove is extended in this portion, the escapedeformation of rubber in an axially outer side direction of the rib ispossible in the vicinity of the side wall of the rib. On the other hand,since the widthwise rigidity in the vicinity of the side wall of the ribis low, the widthwise fine groove is removed from the vicinity of theside wall, whereby the escape deformation of rubber in thecircumferential direction can be allowed while suppressing the loweringof the widthwise rigidity of the rib.

Furthermore, it is preferable that a center line of a rib as a land partrow of a central region located nearest to the equatorial line of thetire is positioned toward the axially inner side with respect to theequatorial line and a plurality of recesses having substantially anellipsoidal form inclusive of oval form or the like are arranged in sucha rib instead of the aforementioned widthwise fine grooves, and a majoraxis of each of recess is extended at an angle of 5-45° with respect tothe widthwise direction of the tread, and a side of a shoulder land partrow located at the axially inner side of the rib is defined by acircumferential main groove extending straightforward.

In order to prevent the wearing of the rib in the vicinity of theequatorial line, it is sufficient to dispose a slight space in the ribso as to form the escape site of rubber in the circumferential directionas previously mentioned. In the central portion of the rib having noescape side of rubber and being less in the contribution to thewidthwise rigidity is arranged the recess having substantially anellipsoidal form instead of the widthwise fine groove, whereby thewidthwise rigidity is ensured while forming the escape site of rubber.

When the direction of the major axis in the recess is less than 5° withrespect to the widthwise direction of the tire, the pattern noisebecomes too large, while when it exceeds 45°, the widthwise rigidity ofthe rib too lowers.

Also, the circumferential main groove defining the rib at the side ofthe shoulder land part row of the axially inner side is rendered into astraight groove, whereby the high resistance to hydroplaning can beproduced.

When a sipe opening to the side wall of the rib is disposed in at leasta part of the plural recesses having substantially an ellipsoidal formso as to extend in the major axis direction of the recess, air sealedand compressed in the recess during the contacting with ground can bedischarged toward an exterior through the sipe, so that it can beprevented to make a sound by releasing air sealed in the recess andhaving a high compression pressure from such a recess in the trailing.

Further, it is preferable that a rib of a land part row of a centralregion located nearest to the equatorial line of the tire is defined bya pair of straight extending circumferential main grooves and a groovewidth of a circumferential main groove located at a side of the shoulderland part row of the axially inner side is made wider than a groovewidth of a circumferential main groove located at a side of the shoulderland part row of the axially outer side.

Considering the difference in the ground contact form of the treadresulted from the difference of aspect ratio or the like of the tire,there is a knowledge that when a maximum width and a maximum length ofthe ground contact form are compared with each other in the actualrunning of the tire under loading, if the maximum width is larger thanthe maximum length, the circumferential main groove drains a greateramount of water as compared with the case that the ground contact lengthbecomes large. According to this knowledge, when the maximum width islarger than the maximum length as in the former case, the drainageproperty can be enhanced to improve the resistance to hydroplaning, forexample, by arranging a greater number of the circumferential grooves inthe tread central portion wherein the flow line direction of thedrainage is substantially the circumferential direction.

Now, it is known that the circumferential main groove forms a columnartube equal to the ground contact length in the ground contact face toresult in the occurrence of columnar resonance sound. The magnificationof the columnar resonance sound differs in accordance with the positionin the widthwise direction of the tread even if the size of the columnartube is same. There is newly obtained a knowledge that when the columnarresonance sound at the axially inner side in which the ground contactlength of the tread becomes long under the application of negativecamber bordering the tread center position is reduced at a greater ratioas compared with the increasing ratio of the columnar resonance sound atthe axially outer side in which the ground contact length becomesshorter toward the side of the tread end. In the invention, the width ofthe circumferential main groove located at the side of the shoulder landpart row in the axially inner side in which the ground contact length ofthe tread becomes long is made wider than that of the othercircumferential main groove, whereby the improvement of the resistanceto hydroplaning is produced while suppressing the occurrence of theresonance sound.

In the tire as mentioned above, when each block defined by the lateralgrooves in the shoulder land part row at the portion of the axiallyouter side is provided with a peripheral upheaved portion graduallydecreasing a surface height toward at least one of a side edge of theblock and a central region of the block, the further improvement of thesteering performance can be realized.

When the tire comprising the blocks provided with the peripheralupheaved portion is run under loading without applying the camber angle,a slant upheaved face of the peripheral upheaved portion isimpact-contacted with the road surface in the leading of the block tocreate a large impact sound.

However, when the peripheral upheaved portion as mentioned above isformed in the shoulder block of the axially outer side in the tire usedunder an application of the negative camber, since the bearing of loadby the outer shoulder block is less during the straight running, theincrease of noise resulted from the presence of the peripheral upheavedportion can be prevented effectively.

On the other hand, when the slip angle is applied to the tire for thesteering, the shoulder portion of the axially outer side is contactedwith ground to increase the ground contact pressure of this portionirrespectively of the presence or absence of the negative camber, sothat the peripheral upheaved portion can uniformize the ground contactpressure distribution of the block under an action inherent to theblock. In the application of the slip angle, the noise due to theslipping of the block becomes predominant and the influence of the noisedue to the impact of the block onto the road surface becomes relativelysmall, so that the steering performance can be effectively improved byarranging the peripheral upheaved portions without increasing the noise.

Preferably, each of leading edge height and trailing edge height in theblocks defined by the slant grooves in at least second inner land partrow is varied in the widthwise direction of the tread, while each highheight portion is extended in the circumferential direction of the treadwhile changing positions in the widthwise direction of the tread inaccordance with the positions in the circumferential direction.

In case of applying the negative camber to the tire, the ground contactlength becomes short and the ground contact pressure becomes low in theportion of the axially outer side, so that the occurrence of strikesound resulted from the impact contact of the block with the roadsurface is relatively less in such outer side portion, while the groundcontact length and ground contact pressure become large in the portionof the axially inner side and the ratio of creating the strike soundbecomes large. In this case, since the land part row in the centralregion is the rib, there is no occurrence of noise due to the impactcontact of the block, and also the inner shoulder land part row isgenerally less in the number of the lateral grooves and small in theratio of creating the strike sound, while the noise created in theblocks defined by the slant grooves in the second inner land part rowbecomes large.

In the invention, therefore, each of leading edge height and trailingedge height in the blocks defined by the slant grooves in at leastsecond inner land part row are varied in the widthwise direction of thetread, while each high height portion is extended in the circumferentialdirection of the tread while changing positions in the widthwisedirection of the tread in accordance with the positions in thecircumferential direction. Thus, firstly, the impact contact of theleading edge with the road surface is gradually carried out for quite along time to disperse the impact contact force with time, whereby theoccurrence of strike noise at an initial contact stage of the block ismitigated. Secondly, the trailing edge is gradually separated apart fromthe road surface for quite a long time to suppress the occurrence of thenoise at the last contact stage. Thirdly, the compression force producedin the block during the running of the tire is dispersedly supportedwith the whole of the block by changing positions in the tread widthwisedirection of each of the high height portions extending in thecircumferential direction of the tread in accordance with thecircumferential positions, whereby noise level produced by the block canbe suppressed.

In other words, when the high height portion is not changed in thewidthwise direction, a large compression stress is locally applied toonly a high height portion of the block and an input level becomeslarge.

In addition to these facts, when each of the high height portionsextending in the circumferential direction of the tread is continued inthe circumferential direction of the tread, the noise level can besuppressed to a low level over a full time ranging from the contact ofthe block with the road surface to the separation from the road surface.

Also, it is preferable that an acute angle corner of a block or the likedefined by at least one of the lateral grooves and slant groovesextending at an average angle of not less than 45° with respect to thewidthwise direction of the tread is provided with a slant face of a flatface, a convex face or the like gradually reducing a height toward atapered end.

In the second inner land part row arranged adjacent to the rib as theland part row of the central region and provided with the slant groovesfor improving the drainage performance, it is effective to make therigidity of the block in the widthwise direction large for enhancing thesteering stability. That is, it is advantageous to make the rigiditydifference to the rib in the second inner land part row adjacent to therib for approaching the increase of cornering force accompanied with theincrease of the slip angle applied to the tire to a linear form. In thiscase, the slant face is formed on the block in the second inner landpart row, whereby the rigidity of the block in the widthwise directionof the tread is enhanced and also the more improvement of the drainageperformance is ensured.

When a projection part projecting into the groove is disposed in agroove wall of the circumferential main groove opposite to a groove wallopening to at least one of the lateral groove and the slant groove at agroove opening position and a position opposite to the widthwisedirection of the tread, as regards the strike sound created resultingfrom the side edge of the land part having a rigidity higher than thatof a groove portion such as lateral groove or the like, the lowering ofthe rigidity in the groove portion such as the lateral groove or thelike is effectively supplemented by the projection portion projectinginto the circumferential main groove to mitigate the rigidity differencebetween the rigidity of a portion forming the groove portion and therigidity of the land part such as block or the like, whereby the strikesound as mentioned above can be advantageously suppressed, which is trueindependently of the application of the negative camber to the tire.

Furthermore, it is preferable that the groove depth of the slant groovearranged in the second inner land part row and extending at an averageangle of not less than 45° with respect to the widthwise direction ofthe tread is deepened gradually or stepwise from a side of theequatorial line of the tire toward a side of the tread end.

In order to improve the drainage efficiency by the slant groove arrangedin the second inner land part row and contributing to the improvement ofthe drainage performance, it is preferable to gradually increase thecross sectional area of the slant groove toward the side of the treadend or render into a sufficiently large constant value. However, inorder to contribute the second inner land part row adjacent to the landpart row of the central region to the improvement of the steeringstability, it is effective to ensure the rigidity of the block or thelike in this land part row in the widthwise direction of the tread at alarge value as previously mentioned. In the invention, therefore, forthe purpose of simultaneously establishing the resistance tohydroplaning and the steering stability at a high dimension, the groovedepth of the slant groove is made shallow at the side of the equatorialline and deepened therefrom toward the side of the tread end, wherebythe cross sectional area is increased toward the side of the tread end.

Now, the extending directions of the slant grooves formed in the secondinner land part row with respect to the equatorial line of the tire maybe the same or may be alternately opposite to each other in thecircumferential direction of the tread.

In case of applying the negative camber to the tire, the slant groovesin the second land part row largely contribute to the improvement of thedrainage performance as previously mentioned. When the tread pattern isa directional pattern specifying the rotating direction, the functionexpected by the slant groove can be sufficiently developed in the formercase that the extending direction of the slant groove with respect tothe equatorial line of the tire is rendered into a given constantdirection.

However, when the tread pattern is a non-direction pattern, the rightand left wheeled tires are relatively rotated in opposite directions. Inthe tire having such a pattern, therefore, it is preferable that theextending directions of the slant grooves are made alternately oppositedirections with respect to the equatorial line of the tire in thecircumferential direction of the tread as in the latter case forensuring the excellent drainage performance even in the rotation of anydirections.

Further, it is preferable that an integral value of the rigidity in thewidthwise direction of the tread over a full ground contact length ineach of the land part rows defined by the circumferential main groovesis within a range of 50% from a large value between mutually adjacentland part rows.

In this case, the rigidity of the shoulder land part row of the axiallyinner side divided by the circumferential fine groove into two parts inthe widthwise direction is defined as a rigidity of only the wide-widthdivided portion located from the fine groove toward the center.

The term “integral value over full contact length” used herein can bedetermined, for example, by measuring a sum of widthwise rigidity ofeach land part row defined by the circumferential grooves over a fullperiphery of the tread, and dividing the ground contact length of such aland part row in the actual mounting by a peripheral length of the landpart row after the filling of an air pressure and multiplying theresulting divided value to the above sum.

More concretely, when one land part row is comprised of, for example, 60mono-pitch blocks, the integral value over the full ground contactlength can be determined by measuring the widthwise rigidity of oneblock, multiplying the measured value to 60 times to determine a sum ofthe rigidity, and multiplying the sum to (number of blocks contactedwith ground/60). On the other hand, when the land part row is comprisedof variable-pitch blocks, the sum of rigidity can be determined bymeasuring the widthwise rigidity of the block having each size,multiplying the number of blocks having each size over the peripherythereto, and adding values of rigidities every each size.

In order to improve the steering performance, it is important that thecornering force produced by applying the slip angle to the tire is largebut also such a cornering force increases at a state near to linearityaccompanied with the increase the slip angle.

When an internal pressure is filled in a tire having a sectional shapeand structure symmetrical with respect to an equatorial plane, a belttension on the equatorial plane becomes frequently highest and also therigidity of the tread becomes maximum at this portion based on such abelt tension. In the straight running of a vehicle under a condition ofapplying no camber to the tire, a longest portion of the ground contactlength positions on the equatorial plane. Therefore, both the beltrigidity and ground contact length become maximum on the equatorialplane, and hence the tread portion on the equatorial plane is a portionproducing a maximum cornering force.

On the other hand, the maximum portion of the ground contact length isnot coincident with the equatorial plane of the tire in the straightrunning under a condition of applying the negative camber. In this case,if the rigidities of the land parts in the tread are the same, a portionhaving a long ground contact length can produce a large cornering force.Also, when the slip angle starts to increase from the straight runningprovided with the camber, it is clear from detailed observations that aportion producing a greatest cornering force is existent between aportion having a maximum belt tension and a portion having a longestground contact length.

As the slip angle is further increased, the longest portion of theground contact length moves toward the outer side of the cornering andthe bearing of load at the outer side of the cornering becomes large. Inthis case, the amount generating the cornering force of the tire at theouter side position of the cornering increases together with theincrease of the ground contact length and the increase of the loadbearing.

Also, such a cornering force is changed due to the fact that therigidity of each land part row in the widthwise direction of the treaddiffers in accordance with the widthwise position of the tread.

For this end, there is examined the relation between the change of therigidity of the land part row in the widthwise direction of the treadand the change of the cornering force. As a result, it has been foundthat the lowering of the rigidity of the land part row in the widthwisedirection generally brings about the lowering of the cornering force,while when the lowering of the rigidity between the mutually adjoiningland part rows is within 50%, the ground contact length of the land partrow is prolonged by the distortion change of such a land part row in theapplication of the slip angle to the tire and hence the lowering of therigidity is compensated by the increase of the ground contact length andthe cornering force can be kept substantially at a constant level. Onthe other hand, when the lowering of the rigidity exceeds 50%, it isimpossible to produce the increase of the ground contact lengthcoincident with the lowering of the rigidity.

In the invention, therefore, the difference of the rigidity in thewidthwise direction of the tread between the mutually adjoining landpart rows is within 50% of a larger value in order to realizesubstantially a linear increase of the cornering force accompanied withthe increase of the slip angle.

At a state that the aforementioned tire is mounted onto an approved rimand inflated under a normal air pressure and loaded under a masscorresponding to the maximum load capacity, an effective ground contactarea at either axially inner side or axially outer side is larger thanthat at the remaining other side, and a radial distance from atangential line on the outer side surface of the tread perpendicular tothe equatorial plane of the tire up to the ground contact edge of thetread at a posture of filling the normal air pressure is made larger atthe mounting side having a small effective ground contact area than atthe other mounting side. This is preferable in a point of controllingconicity force easily produced in a tire of asymmetric pattern. In thiscase, it is more preferable that the relation between a ratio of smalland large effective ground contact areas (S-large/S-small) and a ratioof large and small radial distance (H-large/H-small) satisfiesS-large/S-small=A×(H-large/H-small) wherein A is 1.0-1.4.

In the cornering of the vehicle, it is widely performed that therigidity of the land part at the axially outer side of the tread in thetire existing at the outer side of the cornering, in which the loadparticularly becomes large and the ground contact area increases, ismade larger than that at the axially inner side to enhance the corneringforce. As a concrete construction therefor, it is general that thenegative ratio at the axially outer side is made small to enhance therigidity of the land part, while the negative ratio at the axially innerside is made large to ensure the drainage property.

However, when adopting so-called asymmetric tread pattern having such aconstruction, it is revealed that the ground contact area at the axiallyouter side is made larger than that at the axially inner side, so thatthe widthwise shearing force of the tread contacting face subjected fromthe road surface in the ground contact face of the tire largely differsbetween the axially inner side and the axially outer side in thestraight running of the vehicle, and such a difference causes theoccurrence of conicity force as in the application of the camber angleto the tire to thereby generate lateral force directing to the axiallyouter side in the tire.

As a result of various examinations on the conicity force, it has beenfound that the widthwise shearing force generated in the tread groundcontacting face is largest in the tread shoulder portion and such ashearing force becomes large as the separating distance of the treadground contacting face from the equatorial line of the tire becomeslarge and is very sensitive to the separating distance.

In the asymmetric tread pattern wherein the effective ground contactarea at either axially inner side or axially outer side is made largerthan that at the other position, therefore, the radial distance of fromthe tangential line on the outer side surface of the tread perpendicularto the equatorial plane of the tire up to the ground contact edge of thetread is made larger at the mounting side having a small radial distancethat that at the other mounting side, whereby the widthwise shearingforce produced in the tread shoulder portion at the side having a largeradial distance is contributed to offset the conicity force generated atthe side having the large effective ground contact area and particularlyimprove the steering stability at a small steering angle.

In this case, it is preferable that the conicity force is moreeffectively offset when the relation between a ratio of small and largeeffective ground contact areas (S-large/S-small) and a ratio of largeand small radial distance (H-large/H-small) satisfiesS-large/S-small=A×(H-large/H-small) wherein A is 1.0-1.4.

When A is less than 1.0, the conicity force in the opposite direction iseasily generated, while when it exceeds 1.4, the offset effect of theconicity becomes small.

On the other hand, the invention is made for effectively controlling thetransmission of an input from the road surface to the tire into a wheelshaft when a connecting portion between a rim and a disc of the wheellocates at an outer side of the vehicle mounted with respect to theequatorial plane of the tire mounted onto the rim.

When the connecting portion between the rim and the disc locates at theouter side of the vehicle with respect to the equatorial plane of thetire, a portion of the rim protruding in an inner side direction of thevehicle has a structure as cantilevered by the disc viewing at a radialsection of the wheel, so that the rigidity of the wheel particularlybecomes low against a radial input from the side of the tire to a beadseat of the rim located at the inner side of the vehicle and such aradial input particularly causes a large deformation of the wheel itselfand such a deformation of the wheel is transmitted to a wheel shaft,which is a cause of vibrations on the wheel shaft or the like.Therefore, it is required to control the transmission of the input fromthe road surface into the rim in tires, particularly a tire wherein theground contact pressure and ground contact length become large at theaxially inner side in the application of the negative camber.

In the tire-wheel assembly according to the invention, therefore, theconnecting portion between the rim and the disc of the wheel is locatedtoward the outer side of the vehicle to be mounted with respect to theequatorial plane of the tire when the wheel is assembled with theaforementioned pneumatic tire, particularly the tire wherein theshoulder land part row at the axially inner side is widthwisely dividedinto two parts through the fine groove extending in the circumferentialdirection and the divided part located at the side of the tread end is anarrow-width rib and a plurality of small holes separated from thegroove are formed in the other wide-width divided part which may beprovided with the lateral grooves.

As a result of main studies on solid propagation sound for the purposeof enhancing the silentness in the vehicle interior, it is clear thatvibrations of the wheel largely exerts on the solid propagation sound,which has hitherto been considered to be mainly elastic vibrations ofthe tire consisting of an elastomer such as rubber or the like.

As to the tire vibrations transmitted from the tread portion of the tirethrough a pair of sidewall portions, a pair of bead portions and thewheel toward the vehicle body, as the transmission ratio from eachsidewall portion to the wheel is examined, there is frequently caused adifference between the transmission ratio through the rim end located atthe front side of the wheel disc and the vibration transmission ratiothrough the rim end located at the rear side of the wheel disc, and ithas been confirmed that which side of easily causing wheel shaftvibrations is determined by the connecting position between the rim andthe disc in the wheel irrespectively of an offset amount of the wheeldisc with respect to the rim and hence the equatorial plane of the tire.For example, when the connecting position is existent from theequatorial plane of the tire toward the axially outer side, vibrationsat the axially inner side easily generate vibrations in the wheel shaft.

Therefore, in the shoulder land part row located at the axially innerside of the tire, the compression rigidity is decreased by the smallholes to reduce reaction force against an input from irregularity of theroad surface or the like to the tire, whereby the transmission ofvibrations to the wheel shaft can be suppressed to enhance thesilentness of the vehicle interior. On the other hand, even if therigidity is large and the reaction force against the input to the tirebecomes large in the shoulder land part row located at the axially outerside, the transmission ratio of vibrations from the wheel to the wheelshaft is low in this portion, so that the vibrations of the wheel shaftbecomes not large and the silentness is not damaged.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a developed view of a tread pattern illustrating an embodimentof the invention.

FIG. 2 is a developed view of an other tread pattern.

FIG. 3 is a developed view of further other tread pattern.

FIG. 4 is a view showing a modified example of total volume of smallholes.

FIG. 5 is a schematic view showing an example of forming acircumferential fine groove and a profile form of a side face of anarrow-width rib at a side of a tread end.

FIG. 6 is a schematic view illustrating a profile form of a groundcontact face.

FIG. 7 is a developed view of a tread pattern illustrating anotherembodiment of the invention.

FIG. 8 is a plan view illustrating an example of forming widthwise finegrooves in a land part row of a central region.

FIG. 9 is a view showing a relative relation of a width of acircumferential main groove.

FIG. 10 is a view illustrating an example of forming recesses in a landpart row of a central region.

FIG. 11 is a section view in a widthwise direction of a blockillustrating peripheral upheaved portions.

FIG. 12 is a developed view of a tread pattern showing the otherembodiment.

FIG. 13 is a perspective view showing an example of forming a highheight portion in a block of a second inner side land part row.

FIG. 14 is a developed view of a tread pattern showing the otherembodiment.

FIG. 15 is a developed view showing a further embodiment.

FIG. 16 is a view illustrating a still further embodiment.

FIG. 17 is a developed view of a tread pattern showing a yet furtherembodiment.

FIG. 18 is a schematic view showing integral value of widthwise rigidityin each land part row over a whole of a ground contact length by anindex.

FIG. 19 is a developed view of a tread pattern showing an otherembodiment.

FIG. 20 is a view illustrating a modified example of a tread pattern.

FIG. 21 is a schematic view showing a tire construction for suppressingconicity force.

FIG. 22 is a section view of a main part showing an embodiment of thetire-wheel assembly.

FIG. 23 is a developed view of a tread pattern in a tire of ComparativeExample 1.

FIG. 24 is a developed view of a tread pattern in a tire of ComparativeExample 2.

FIG. 25 is a developed view of a tread pattern in a tire of Example 2.

FIG. 26 is a developed view of a tread pattern in a tire of ComparativeExample 6.

FIG. 27 is a developed view of a tread pattern in a tire of ComparativeExample 7.

FIG. 28 is a developed view of a tread pattern in a tire of Examples 13and 16.

FIG. 29 is a developed view of a tread pattern in a tire of Example 14.

FIG. 30 is a developed view of a tread pattern in a tire of Examples 15and 17.

FIG. 31 is a developed view of a tread pattern in a tire of Example 18.

FIG. 32 is a developed view of a tread pattern in a tire of Example 19.

FIG. 33 is a developed view of a tread pattern in a tire of Example 20.

FIG. 34 is a developed view of a tread pattern in a tire of Example 21.

FIG. 35 is a developed view of a tread pattern in a tire of Example 5.

FIG. 36 is a developed view of a tread pattern in a tire of Example 22.

FIG. 37 is a developed view of a tread pattern in a tire of ComparativeExample 10.

BEST MODE FOR CARRYING OUT THE INVENTION

In a developed view of a tread pattern shown in FIG. 1, E is anequatorial line of a tire.

Moreover, the internal structure of this tire is the same as in ageneral radial tire, and an illustration thereof is omitted here.

In a tread contacting face 1 are formed four circumferential maingrooves 2, 3, 4, 5, which are located asymmetrically with respect to theequatorial line E of the tire and extend linearly and continuously in acircumferential direction, whereby there are defined one central regionland part row located nearest to an equatorial line E and adjacent to aleft side of the main groove inclusive of the equatorial line E in thisfigure, and two land part rows consisting of a shoulder land part row 7located at a side of a tread end and a second inner land part row 8located between the shoulder land part row 7 and the central region landpart row 6 in a left-half side region of the figure being an axiallyinner side mounted onto a vehicle, and two side region land part rowsconsisting of a shoulder land part row 9 and a second outer land partrow 10 located between the shoulder land part row 9 and the centralregion land part row 6 in a right-half portion of the figure being anaxially outer side.

In the illustrated embodiment, the central region land part row 6 andthe shoulder land part row 7 at the axially inner side are rendered intoribs, respectively, and the shoulder land part row 9 at the axiallyouter side is rendered into a block row consisting of blocks 12 definedby lateral grooves 11 extending at an average angle of preferably notmore than 15° with respect to a widthwise direction of the tread, whilea sum of groove volume in the circumferential direction per unit widthof lateral grooves, which may be formed in the shoulder land part row 7of the axially inner side, is made smaller than a sum of groove volumein the circumferential direction of the lateral grooves 11 formed in theshoulder land part row 9 of the axially outer side.

In the second inner land part row 8 are arranged a plurality of slantgrooves 13 extending at an average extending angle of not less than 45°with respect to the widthwise direction of the tread in the sameextending direction as the lateral grooves 11, and these slant grooves13 are opened at least to the circumferential main groove 2 located atthe side of the shoulder land part row of the axially inner side.Therefore, the other end of the slant groove 13 may be terminated in theland part row as shown in the figure, or may be opened to thecircumferential main groove 3 located at the side of the central regionland part row.

In the second outer land part row 10 are arranged a plurality of lateralgrooves 14 extending in the same direction as in the lateral grooves 11and the slant grooves 13 and opening to the adjoining circumferentialmain grooves 4, 5, respectively, whereby the land part row 10 isrendered into a block row consisting of blocks 15.

Moreover, the lateral groove 14 may be opened at either one end to thecircumferential main groove and terminated at the other end in the landpart row. In this case, as shown in FIG. 2, it may be opened to thecircumferential main groove 5 located at the side of the shoulder landpart row of the axially outer side or may be inversely opened to onlythe circumferential main groove 4.

In the rib of the central region land part row may be arranged sipes 16extending in a direction crossing the rib for enhancing the groundcontacting property and ensuring an edge component in the widthwisedirection of the tread.

FIG. 3 is a developed view of a tread pattern illustrating anotherembodiment.

In this case, three or more circumferential main grooves, four grooves2-5 in the figure continuously extending straightforward in acircumferential direction of a tread are formed in the treadasymmetrically with respect to the equatorial line E of the tire,whereby there are defined a central region land part row 6 locatednearest to the equatorial line E and extending on the equatorial line inthe figure, two land part rows consisting of a shoulder land part row 7located at a side of a tread end and a second inner land part row 8located between the shoulder land part row 7 and the central region landpart row 6 in a left-half side region being an axially inner side in thefigure, and two land part rows consisting of another shoulder land partrow 9 located at a side of a tread end and a second outer land part row9 located between the shoulder land part row 9 and the central regionland part row 6 in a right-half side region being an axially outer sidein the figure.

In this figure, the central region land part row 6 somewhat biasedtoward to the axially inner side is rendered into a rib, while theshoulder land part row 7 of the axially inner side is divided into twoportions in the widthwise direction of the tread through a fine groove17 extending in the circumferential direction of the tread wherein adivided portion located to a side of the tread end is a narrow-width rib18 and a divided portion located near to the tread center is awide-width rib 19 somewhat wider than the above divided portion.

A total volume of lateral grooves, which may be formed in the wide-widthrib 19 but is not formed in the figure, per unit width in thecircumferential direction of the tread is made smaller than that ofplural lateral grooves 11 formed in the shoulder land part row 9 of theaxially outer side, and an average extending angle of the lateral groove11 with respect to the widthwise direction of the tread is preferablynot more than 15°.

Further, a plurality of small holes 20 separated from the groove areformed in the wide-width rib 19. Preferably, a total volume of thesesmall holes 20 in the circumferential direction of the tread is madelarger at a side of the fine groove 17 than at a side of the treadcenter as shown, for example, in FIG. 4.

Moreover, the total volume of the small holes 20 is made larger at theside of the fine groove by making the forming density of the small holes20 large at the side of the fine groove in this figure. Alternatively orin addition thereto, the required total volume may be obtained by makingat least one of hole diameter and hole depth large at the side of thefine groove.

As shown by a cross-sectional view in FIG. 5, the groove width of thecircumferential main groove 17 formed in the shoulder land part row 7 ofthe axially inner side is preferable to be gradually or stepwise widenedtoward a side of the tread surface. Also, in the narrow-width rib 18divided and formed by the fine groove 17, a side face thereof at thetread end face is preferable to be a concave curved form having a centerof curvature at an outer side of a cross-sectional profile line asillustrated in FIG. 5.

More preferably, the tread and hence the tread contacting face is soconstructed that at least a part of the small hole forming region in thewide-width rib 19 is included in a ground contact region enclosed by aground contact profile line in FIG. 6 under an action of a loadcorresponding to 40% of a maximum load capacity during the rotation ofthe tire at a camber angle of −0.5° under loading.

In addition, a plurality of slant grooves 13 extending at an averageangle of preferably not less than 45° with respect to the widthwisedirection of the tread are formed in the second inner land part row 8,and these slant grooves 13 are at least opened to the circumferentialmain groove 2 extending at the side of the tread end.

The slant groove 13 opened at both ends to the mutually adjoiningcircumferential main grooves 2, 3 in the figure may develop sufficientdrainage performance in a tire of a directional pattern in which therotating direction of the tire is specified into one direction when theinclination direction of the groove with respect to the equatorial lineE is constant, but in a tire not specifying the rotating direction, itis preferable that the extending directions of the slant grooves withrespect to the equatorial line E of the tire are opposite to each otherin the circumferential direction as shown in the figure in order toensure the drainage performance even in any rotating directions.

Also, it is preferable that the depth of the slant groove is graduallydeepened from the side of the equatorial line of the tire toward theside of the tread end in order to simultaneously establish thesufficient drainage performance and the high land part rigidity.

Furthermore, in connection with the slant groove 13 extending at anaverage angle of not less than 45° with respect to the widthwisedirection of the tread and the other lateral grooves, it is preferablethat a slant face 21 gradually decreasing a height toward a top andhaving a flat face, a convex curved face or the like as shown by obliquelines in the figure is formed in an acute corner part of a blocksandwiched between the slant groove and the circumferential groove, atleast an acute corner part located at the side of the equatorial line ofthe tire as shown in FIG. 3, whereby it is attempted to improve thedrainage property while ensuring the rigidity of the acute corner part.

Moreover, as shown in FIG. 3, a plurality of lateral grooves 14 openingat one end to the circumferential groove and terminating at the otherend in the land part row are arranged in the second outer land part row10 so as to alternately open to the adjoining circumferential maingrooves 4, 5 in the circumferential direction of the tread.

FIG. 7 is a developed view of a tread pattern illustrating the otherembodiment wherein a widthwise center line C of the central region landpart row 6 is biased to a direction of the axially inner side in whichthe ground contact length of the tread becomes long through theapplication of a camber angle with respect to the equatorial line E ofthe tire and a plurality of widthwise fine grooves 22 extending at anaverage angle of 5-45° with respect to the widthwise direction of thetread and having a groove width of not more than 2 mm are formed in theland part row 6 to allow circumferential deformation of the land partrow 6 as a rib.

In this case, an arranging pitch of these widthwise fine grooves 22alternately extending opposite to each other in the circumferentialdirection for ensuring a rigidity balance of the land part row 6 or thelike can be selected by considering escape deformation of rubber in thecircumferential direction and reservation of widthwise rigidity.

At least a part of the thus formed widthwise fine grooves 22 may beterminated at both ends in the rib. Also, each of the fine grooves 22 ispreferable to be formed so as to incline in a depth direction in form ofa flat face, a curved face or the like provided that the fine groove isseparated away from each other in a groove width direction as shown byoblique lines in partial perspective views of FIGS. 8(a) and (b).

Moreover, the inclination direction may be a circumferential direction,a direction perpendicular to the opening of the fine groove or the like,and also three or more inclined portions may be formed in one finegroove 22.

As to the pair of straight circumferential main grooves 3, 4 definingthe central region land part row 6, it is preferable that the groovelocated at the side of the second inner land part row 8 is made widerthan the groove located at the side of the second outer land part row 10as shown in FIG. 9, whereby the drainage property is enhanced tosuppress the columnar resonance sound.

FIG. 10 is a view of a main part of the other embodiment, in which acenter line C of the central region land part row 6 is biased toward aside of prolonging the ground contact length by the application of acamber angle with respect to the equatorial line E, and a plurality ofrecesses 23 having substantially an ellipsoidal form are formed in theland part row as a rib at a posture of inclining a major axis at anangle of 5-45° with respect to the widthwise direction of the tread andthe extending directions of the major axes of these recesses 23 arealternately opposed in the circumferential direction of the tread andfurther a portion of the land part row 6 located at the side of thesecond inner land part row 8 is defined by the circumferential maingroove 3 linearly extended.

Moreover, the recess is possible to be an oval form or the like. Asshown in FIG. 10(b), at least a part of the recesses 23 may be providedat both ends of the major axis with sipes 24 extending in the major axisdirection of the recess 23. Also, the sipe 24 may be arranged only atthe one end side of the recess, or the length of the sipe 24 may beterminated in the land part row or opened to the circumferential maingroove.

In the tire as mentioned above, each of the blocks 12 defined in theshoulder land part row of the axially outer side by the lateral grooves11 may be provided with a peripheral upheaved portion 25 graduallydecreasing a surface height toward at least one of a side edge of theblock and a central region of the block as shown by a widthwisesectional view in FIG. 11, toward both in the figure. The peripheralupheaved portion 25 functions to uniformize the ground contact pressurein the contacting of the block 12 with ground.

FIG. 12 is a developed view of a tread pattern illustrating the otherembodiment.

In this case, a circumferential fine groove 17 is formed in the shoulderland part row 7 of the axially inner side to divide the shoulder landpart 7 into a narrow-width rib 18 located at the side of the tread endand a wide-width rib 19 located at the side of the equatorial line, andslant grooves 13 extending at an equal inclination angle in the samedirection are formed in the second inner land part row 8 and opened tothe circumferential main grooves 2, 3 to render the land part row 8 intoa block row consisting of blocks 26, and lateral grooves 11 in theshoulder land part row 9 of the axially outer side are extendedsubstantially in the widthwise direction of the tread.

When the second inner land part row 8 is rendered into the above blockrow, each height of a leading edge 26 and a trailing edge 27 in eachblock 26 constituting the block row is varied in the widthwise directionof the tread as shown by a schematic perspective view in FIG. 13(a),while each high height portion can be extended in the circumferentialdirection of the tread while changing positions in the widthwisedirection of the tread in accordance with the positions in thecircumferential direction as shown by oblique lines in the figure. Inthis case, it is preferable that both the heights are continuouslyformed in the circumferential direction of the tread as shown in thefigure.

In the illustrated embodiment, the high height portion of the leadingedge 27 first contacting with ground is biased toward the side of theequatorial line of the tire, and also the high height portion of thetrailing edge 28 latest separating from the road surface is biasedtoward the shoulder side of the axially inner side, but the biasingdirections of these height portions can be opposed thereto. Also, theextending form of the high height portion in the circumferentialdirection of the tread is rendered into a bending form as shown in FIG.13(b), whereby the high height portions of the leading edge 27 and thetrailing edge 28 can be biased toward the shoulder side of the axiallyinner side, or both the portions can be biased in an opposite directionthereto.

Furthermore, the extending form of the high height portion can berendered into a zigzag form as shown in FIG. 13(c).

FIG. 14 is a view illustrating a further embodiment, in which the slantgrooves 13 formed in the second inner land part row 8 are extended inthe form convexly curving downward in the figure, while a slant face 29gradually decreasing a height toward a tapered end as shown by obliquelines in the figure is formed in an acute corner portion of each block26 sandwiched between the slant groove 13 and the circumferential maingroove 3, whereby the rigidity of the block 26, particularly the acutecorner portion thereof in the widthwise direction of the tread can beenhanced, and the volume of the groove portion can be substantiallyincreased.

Such a slant face can be formed in the block or the like other than theblock 26. This is particularly effective with respect to the acutecorner portion defined by the lateral groove, slant groove or the likeextending at an average angle of not less than 45° with respect to thewidthwise direction of the tread and the circumferential main groove.

Moreover, numeral 30 is a sipe formed in the wide-width rib 19 in theshoulder land part row 7 of the axially inner side.

FIG. 15 is a view illustrating a still further embodiment. In thecircumferential main groove 3 located at the side of the equatorial lineof the tire opening the slant groove 13 formed in the second inner landpart row 8, a projection part 32 projecting into the groove isintegrally disposed on the groove bottom in a groove wall 31 of thecircumferential main groove 3 opposite to a groove wall opening to theslant groove 13 at an opening position of the groove 13 opposite to thewidthwise direction of the tread. According to this embodiment, thedifference of rigidity in the second inner land part row 8 due to thepresence of the slant groove 13 during the running of the tire underloading can be mitigated by the projection parts 32 to reduce the strikesound of the edge of the slant groove 13 on the road surface.

In the illustrated embodiment, the projection part 32 is arranged onalternate opening of the slant groove to the circumferential main groove3, but the projection part 32 may be arranged in positions correspondingto all openings. Also, the projection part may be arranged incorrespondence with the opening position of the other lateral groove.

In an embodiment shown in FIG. 16, a width of the slant groove 13 formedin the second inner land part row 8 and extending curvedly in a convexform downward in the figure is made narrower than that shown in FIG. 14,and a depth thereof is gradually deepened from the side P₁ of theequatorial line of the tire toward the side P₂ of the tread end as shownby a graph in FIG. 16(b).

In an embodiment of FIG. 17, the extending directions of the slantgrooves 13 formed in the second inner land part row 8 with respect tothe equatorial line of the tire are opposite to each other in thecircumferential direction of the tread likewise FIGS. 3, 6, 7 and thelike, and also one end of each of the lateral grooves 14 formed in thesecond outer land part row 10 is alternately opened to thecircumferential main grooves 4, 5 sandwiching the outer land part row 10in the circumferential direction of the tread and the other end thereofis terminated in the land part, and further sipes 30 alternatelychanging the inclination direction in the circumferential direction areformed in the wide-width rib 19 of the shoulder land part row 7 of theaxially inner side as shown in FIG. 14.

In each of the thus constituted land part rows, an integral value of therigidity in the widthwise direction of the tread over a full groundcontact length is within a range of 50% from a large value betweenmutually adjacent land part rows.

FIG. 18 is a view showing the above case by a rigidity index, in whichthe rigidity indexes of the land part rows are 90, 60, 100, 110 and 120in order from the shoulder land part row of the axially inner sidelocated at the left side of the figure.

FIG. 19 shows a further embodiment in which a sum of extendingcomponents in the widthwise direction of the tread of edges, which maybe particularly formed in the shoulder land part row of the axiallyinner side, edges 34 formed by the lateral grooves 33 in the shoulderland part 7 in the figure is made smaller than a sum of extendingcomponents in the widthwise direction of the tread of edges 35 formed bythe lateral grooves 11 in the shoulder land part row 9 of the axiallyouter side and at the same time a plurality of slant grooves 13extending at an average angle of not less than 45° with respect to thewidthwise direction of the tread and opening to at least thecircumferential groove 1 are formed in the second inner land part row 8.

In the embodiment of this figure, all of the lateral grooves 14 formedin the second outer land part row 10 are opened to only thecircumferential groove 5 at the side of the tread end and the other endsthereof are terminated in the land part row.

FIG. 20 shows a modified example of the above case, in which sipes 36are formed in the wide-width rib 19 divided by the fine groove 17 in theshoulder land part row 7 of the axially inner side instead of the abovelateral grooves 23 to form edges with these sipes 36, while sipes 37 areformed in the shoulder land part row 9 of the axially outer side inaddition to the lateral grooves 11 to form edges with these sipes andgrooves.

In the asymmetrical pattern tires as mentioned above, in order tosuppress the occurrence of conicity force directing to a direction ofthe axially outer side when an effective ground contact area S_(out) ofthe outer side mounting portion shown by oblique lines in the figure ismade larger than an effective ground contact area S_(in) of the innerside mounting portion by differing the negative ratio between the innerside mounting portion and the outer side mounting portion in the treadground contact face under a condition that the tire is mounted onto anapproved rim and inflated under a defined air pressure and loaded undera mass corresponding to a maximum load capacity as the tread groundcontact face is schematically shown in FIG. 21(a), the tire is effectiveto be constituted by selecting an inner surface form of a vulcanizationmold or the like so that radial distances H_(in), H_(out) fromtangential line T on an outer surface of the tread perpendicular to anequatorial plane EP of the tire to ground contact edges EI and EO of thetread become large in the axially inner side having a small effectiveground contact area (H_(in)>H_(out)) as shown by a schematically sectionview in the widthwise direction of the tire at a state of inflatingunder a normal air pressure in FIG. 21(b).

This is true in case of setting the magnitude relation of the effectiveground contact area opposite to the above. In the latter case, the tireis constituted in such a manner that the radial distances H_(in),H_(out) satisfy the relation of H_(out)>H_(in).

In this case, it is more preferable to satisfy a relation ofS-large/S-small=A×(H_((S-small side))/H_((S-large side))) in which A is1.0-1.4 when a large effective ground contact area is S-large and asmall ground contact area is S-small and a radial distance at a side oflarge effective ground contact area is H_((S-large side)) and a radialdistance at a small side is H_((S-small side)).

FIG. 22 is a section view of a main part illustrating an embodiment ofthe tire-wheel assembly according to the invention. In case of mountingthe aforementioned tire in which the compression rigidity of theshoulder land part row in the axially inner side is small onto a wheel,a connection part 41 between a rim 39 and a disc 40 in a wheel 38 islocated at an outer side of a vehicle to be mounted with respect to theequatorial plane EP of the tire.

According to this embodiment, the transmission of vibrations from thetire to an axle can be advantageously controlled based on the loweringof the compression rigidity of the shoulder land part row of the axiallyinner side.

EXAMPLE 1

Each of example tires and comparative example tires having a tire sizeof 225/55 R16 is assembled onto a rim of 7.0J-16 and filled under an airpressure of 210 kPa and mounted onto a vehicle. The vehicle is actuallyrun at a state of two crewmen riding under a condition that a negativecamber of a front wheel is 0.3° and a negative camber of a rear wheel is0.5°, during which a wear ratio of shoulder land part rows, a speedgenerating a hydroplaning phenomenon, a vehicle interior noise and asteering stability on a dry road surface are measured.

Example tire 1 has a tread pattern shown in FIG. 1, in which a slantgroove in a second inner land part row has an angle of 45° with respectto a widthwise direction of a tread and an extending angle of a lateralgroove in a second outer land part row is 30° and an average extendingangle of a lateral groove in a shoulder land part row of an axiallyouter side is 15°.

Example tire 2 has a tread pattern shown in FIG. 2, in which an angle ofeach groove is the same as in Example tire 1.

Example tire 3 has a tread pattern shown in FIG. 12 in which anextending angle of a slant groove in a second inner land part row is 50°and an angle of a lateral groove in a second outer land part row is 30°and an angle of a lateral groove in a shoulder land part row of anaxially outer side is 0°.

Example tire 4 has a tread pattern shown in FIG. 1 in which the grooveangle is the same as in Example tire 1 and a peripheral upheaved portionas shown in FIG. 11 is provided on a block in a shoulder land part rowof an axially outer side.

Example tire 5 has a tread pattern shown in FIG. 12 in which the grooveangle is the same as in Example tire 3 and a high height portion of anextending embodiment shown in FIG. 13(a) is provided on a block in asecond inner land part row.

Example tire 6 has a tread pattern shown in FIG. 14 in which an averageangle of a slant groove in a second inner land part row is 60° and anangle of a lateral groove in a second outer land part row is 30° and anangle of a groove in a shoulder land part row of an axially outer sideis 0°.

Example tire 7 has a tread pattern shown in FIG. 15 in which an angle ofa slant groove in a second inner land part row is 45° and an angle of alateral groove in a second outer land part row is 30° and an angle of agroove in a shoulder land part row of an axially outer side is 0°.

Example tire 8 has a tread pattern shown in FIG. 16 in which an averageangle of a slant groove in a second inner land part row is 60° and adepth of the slant groove is changed from 2.0 mm to 6.5 mm and an angleof a lateral groove in a second outer land part row is 30° and an angleof a lateral groove in a shoulder land part row of an axially outer sideis 0°.

Example tire 9 has a tread pattern shown in FIG. 17 in which an angle ofa slant groove in a second inner land part row is ±50° and an averageangle of a lateral groove in a second outer land part row is 30° and anangle of a lateral groove in a shoulder land part row of an axiallyouter side is 0°.

Comparative Example tire 1 has a tread pattern shown in FIG. 23 in whichan angle of a lateral groove in a shoulder land part row of an axiallyinner side is 10° and an angle of a slant groove in a second land partrow is 50° and an angle of a lateral groove in a second outer land partrow is 30° and an angle of a lateral groove in a shoulder land part rowof an axially outer side is 10°.

Comparative Example tire 2 has a tread pattern shown in FIG. 24 in whichan angle of a slant groove in a second inner land part row is 40° and anangle of a lateral groove in a second outer land part row is 30° and anangle of a lateral groove in a shoulder land part row of an axiallyouter side is 17°.

Test Method

Wear Ratio

After the running over 2000 km at a ratio of express way,general-purpose road and mountain path of 50%, 40% and 10%, worn amountsof widthwise central portions of both shoulder land part rows aremeasured, from which a ratio of both is determined for evaluation. Acase that the axially inner side is largely worn is shown by a numericalvalue of not more than 1, while a case that the axially outer side islargely worn is shown by a numerical value of not less than 1. Moreover,a preferable range of the wear ratio is 1.0-1.2.

Speed Generating Hydroplaning Phenomenon

The speed generating the hydroplaning phenomenon is evaluated by a testdriver when an acceleration test is carried out from a speed of 50 km/hin a pool having a water depth of 6 mm. The result is represented by anindex of an average speed generating hydroplaning phenomenon on left andright wheels and is better as the index value becomes large.

Vehicle Interior Noise

A noise level is measured on a microphone placed at a side of a centralpart of the vehicle about a driver's ear during the running at aconstant speed of 60 km/h on a smooth road surface of a test circuitcourse. The noise is represented by an index in which the larger theindex value, the lower the noise.

Steering Stability

It is evaluated by a driver's feeling during the running on a dry roadsurface of a test circuit course. The result is represented by an index,in which the larger the index value, the better the result.

These test results are shown in Table 1. TABLE 1 Speed Wear generatingSteering FIG. ratio hydroplaning Noise stability Comparative 0.9 110 100100 Example tire 1 Comparative 1.0 100 110 90 Example tire 2 Exampletire 1 1.0 110 101 110 Example tire 2 1.0 105 110 110 Example tire 3 1.1115 110 120 Example tire 4 FIG. 1 + FIG. 11 1.0 110 101 125 Example tire5 FIG. 12 + 1.1 115 125 120 FIG. 13(a) Example tire 6 1.05 120 110 125Example tire 7 1.1 112 115 110 Example tire 8 1.1 115 113 125 Exampletire 9 1.05 125 105 110

As seen from Table 1, in the example tires, the excellent resistance touneven wear can be ensured while effectively attaining the improvementof the resistance to hydroplaning, the reduction of the vehicle interiornoise and the improvement of the steering stability.

EXAMPLE 2

Each of example tires and comparative example tires having a tire sizeof 215/45 R17 and a tread pattern shown in FIG. 25 is assembled onto arim of 7.5J×17 and filled with an internal pressure of 220 kPa, and acamber angle of −0.5° is applied to make a ground contact length of anaxially inner side long, and thereafter a slip angle is changed from 0degree to 5 degrees at a speed of 30 km/h to measure a cornering forcegenerated.

When a difference of cornering force between 0 degree and 1 degree isCf1 and a difference of cornering force between 0 degree and 2.5 degreesis Cf2 and a difference between 0 degree and 5 degrees is Cf3, ifCf2/Cf1 is 2.5 and Cf3/Cf1 is 5, the cornering force is linearlygenerated, while if Cf2/Cf1 is larger than 2.5, the cornering forceincreases non-linearly at a position having a large slip angle, and ifCf2/Cf1 is smaller than 3, the cornering force decreases non-linearly.

In these tires, an integral value of rigidities of the land part rowsshown in FIG. 25 in the widthwise direction of the tread is representedby an index in Table 2, and a ratio of cornering forces measured isshown in Table 3.

Moreover, the index value in Table 2 shows that the value is large asthe rigidity becomes high. TABLE 2 Second Second Vicinity outer inner ofcon- Inner stretching central tracting Outer shoulder side portion sideshoulder Comparative 210 100 100 100 210 Example tire 3 Comparative 180100 100 210 450 Example tire 4 Comparative 50 80 100 110 50 Example tire5 Example tire 10 100 100 100 100 100 Example tire 11 180 100 100 100 80Example tire 12 80 50 100 100 100

TABLE 3 Cf2/Cf1 Cf3/Cf1 Comparative Example tire 3 2.5 5.5 ComparativeExample tire 4 3.0 5.8 Comparative Example tire 5 2.5 4.5 Example tire10 2.5 5.0 Example tire 11 2.5 5.1 Example tire 12 2.6 5.0

As seen from Table 3, all of Example tires 10-12 can increase thecornering force substantially linearly, while the cornering forcebecomes non-linear at a position having a large slip angle inComparative Example tires 3 and 5 and at a position having a small slipangle in Comparative Example tire 4.

EXAMPLE 3

Each of example tires and comparative example tires having a tire sizeof 235/45 R17 is assembled onto a rim of 8J×17 under an internalpressure of 210 kPa and mounted onto a vehicle in which a camber angleat a front wheel is −0.4° and that at a rear wheel is −0.6° at a stateof two crewmen riding.

This vehicle is subjected to a wearing test. The test condition is thatit is run on an expressway, a general purpose road and a mountain pathat a ratio of 50%, 40% and 10% over 20000 km. After the running, a ratioof worn amounts of widthwise central portions of both shoulder land partrows in two front wheels is measured. A case that the ratio is largerthan 100 shows that the axially inner side is largely worn, and a casethat the ratio is smaller than 100 shows that the axially outer side islargely worn.

The vehicle is subjected to an acceleration test from a speed of 50 km/hin a pool having a water depth of 6 mm to thereby evaluate a speedgenerating hydroplaning by a test driver. The result is represented byan index of an average speed generating hydroplaning phenomenon on leftand right wheels and is better as the index value becomes large.

A noise is measured in the vehicle on a smooth road surface of a testcircuit course. It is measured by a microphone placed at a centralportion of the vehicle about a driver's ear during the running at aconstant speed of 60 km/h. The noise is represented by an index, inwhich the larger the index value, the lower the noise.

These test results are shown in Table 4.

Comparative Example tire 6: has a tread pattern shown in FIG. 26 whereinlateral grooves having an angle of 12° with respect to the widthwisedirection are formed in a shoulder land part row of an axially innerside and slant grooves having an angle of 55° are formed in a secondinner land part row, and a central region is a rib, and lateral grooveshaving an angle of 35° are formed in a second outer land part andlateral grooves having an angle of 12° are formed in an outer shoulderland part row.

Comparative Example tire 7: has a tread pattern shown in FIG. 27 whereina shoulder land part row of an axially inner side is a rib and slantgrooves having an angle of 42° are formed in a second inner land part,and sipes are formed in a rib of a central region, and lateral groovesextending at an angle of 32° and opening to only an axially outer sideare formed in a second outer land part row and lateral grooves having anangle of 32° are formed in a shoulder land part row of the axially outerside.

Example tire 13: has a tread pattern shown in FIG. 28 wherein a shoulderland part row of an axially inner side is a rib and slant grooves havingan angle of 42° are formed in a second inner land part, and sipes areformed in a rib of a central region, and lateral grooves having an angleof 32° are formed in a second outer land part row and lateral groovescurving convexly upward and having an average angle of 12° are formed ina shoulder land part row of an axially outer side.

Example tire 14: has a tread pattern shown in FIG. 29, which isdifferent from the example tire 13 in only a point that the lateralgroove in the second outer land part row is opened only to the axiallyouter side.

Example tire 15: has a tread pattern shown in FIG. 30 wherein a shoulderland part of an axially inner side is divided into two parts and slantgrooves having an angle of 55° are formed in a second inner land partrow, and a sipes are formed in a rib of a central region, and lateralgrooves having an angle of 32° and formed in a second outer land partrow are opened only to an axially outer side and lateral grooves havingan angle of 5° are formed in a shoulder land part row of the axiallyouter side.

Example tire 16: has a tread pattern shown in FIG. 28, which isdifferent from the example tire 13 in points that an angle of the slantgroove formed in the second inner land part row is 45° and a peripheralupheaved portion shown in FIG. 11 is provided on a block of the outershoulder land part row.

Example tire 17: has a tread pattern shown in FIG. 30, which isdifferent from the example tire 15 in a point that heights of leadingedge and trailing edge in a land part of each of the second inner landpart row and the second outer land part row differ in the widthwisedirection of the tread and each of high height portions is extendedlinearly in a circumferential direction of the tread while changingpositions in the widthwise direction of the tread in accordance with thecircumferential positions and continued in the circumferentialdirection.

Example tire 18: has a tread pattern shown in FIG. 31, which is the sameas Example 15 except points that sipes are formed in a wide-width rib ofa shoulder land part of the axially inner side and the slant grooveformed in the second inner land part row is a downward convex curve atan average extending angle of 60° and a slant face gradually decreasinga height toward a top end side is formed in an acute corner part of ablock defined by the slant grooves.

Example tire 19: has a tread pattern shown in FIG. 32, which is the sameas in FIG. 31 except that projection parts are arranged on a side wallof a central region rib in correspondence with positions of slantgrooves of 45° formed in a second inner land part row and opening to theside of the central region rib and at a pitch corresponding to twoopenings.

Example tire 20: has a tread pattern shown in FIG. 33, which is the sameas in FIG. 30 (Example tire 15) except that a slant groove formed in thesecond inner land part row is a downward convex curve at an averageextending angle of 60° and a depth of the slant groove is 2 mm at an endof a tread center side and is gradually deepened toward a side of atread end and is 6.5 mm at an opening end to the circumferential maingroove located at the shoulder side.

Example tire 21: has a tread pattern shown in FIG. 34, wherein sipes areformed in a wide-width rib divided in a shoulder land part row of anaxially inner side and slant grooves are formed in a second inner landpart row at an angle of 50° and the extending directions thereof arealternately opposed to each other in the circumferential direction, andsipes are formed in a central region rib, and one end of a lateralgroove formed in a second outer land part row is alternately opened tothe adjoining circumferential grooves in the circumferential directionand the other end thereof is terminated in the land part row, and anangle of a lateral groove formed in an outer shoulder land part row is5°. TABLE 4 Wear Resistance to Steering FIG. ratio hydroplaningSilentness stability Comparative 115 100 100 100 Example tire 6Comparative 92 90 100 95 Example tire 7 Example tire 13 97 105 101 105Example tire 14 97 105 105 105 Example tire 15 100 110 105 110 Exampletire 16 FIG. 28 + 97 105 101 112 Example tire 17 FIG. 30 + 100 110 112110 FIG. 13(a) Example tire 18 99 112 105 125 Example tire 19 98 107 103105 Example tire 20 98 110 103 125 Example tire 21 100 113 103 105

EXAMPLE 4

PSR 205/65R15, rim: 6JJ×15, internal pressure: 200 kPa, two load levelsof 0.588 kN and 0.235 kN.

There are carried out indoor wear test on a shoulder land part row of anaxially inner side at a camber of 0.5 degree and an indoor test ofgenerating a hydroplaning phenomenon.

Also, the number of foreign matters such as stones or the like bitten infine grooves formed in the shoulder land part row of the axially innerside is measured after the running of a vehicle on general-purpose roadover 1000 km.

Comparative Example tire 8: A pattern is similar to that of FIG. 35,wherein a center line of a rib in a central region is coincident with anequatorial line of the tire, and small holes are not formed in ashoulder land part row of an axially inner side, and a width of a finegroove in a circumferential direction of the shoulder is substantiallyconstant in a depth direction, and lateral grooves extending at an angleof 5° in the widthwise direction are formed in a shoulder land part rowof an axially outer side.

Moreover, this tire is included in the invention of claim 1.

Example tire 22: has a pattern shown in FIG. 36, wherein small holesformed in a shoulder land part row of an axially inner side are dense ata shoulder side and rough at a center side as shown in FIG. 4, andthree-dimensional sipes of three-divided type shown in FIG. 8(b) areformed in a central land part row, and a width of a circumferential finegroove in a shoulder is gradually decreased from a surface toward bottomso as to be 3 mm at a surface of a new tire tread and 0.5 mm at a groovebottom.

The performance is represented by an index in Table 5 using thecomparative example tire 8 as a control, in which the larger the indexvalue, the better the result. TABLE 5 Wear Wear Number (load: (load:Hydro- of foreign FIG. 0.588 kN) 0.235 kN) planing matters Comparative100 100 100 100 Example tire 8 Example tire 22 110 108 110 670

EXAMPLE 5

After each of example tires and comparative example tire having a tiresize of 215/45 R17 is assembled onto a standard rim and adjusted to 220kPa, the resistance to hydroplaning and steering stability in straightrunning on a test circuit course are evaluated by feeling and the wornamount of a tread center portion is measured by running the vehicle over20000 km as to center wearing. The results are shown in Table 6 using acomparative example tire 11 as a control.

Comparative Example Tire 9

It has a tread pattern shown in FIG. 35 wherein a central region landpart row is a rib having a width of 18 mm.

Moreover, this tire is included in the invention of claim 1 aspreviously mentioned.

Example Tire 23

In a tread pattern shown in FIG. 35, a plurality of sipes extending atan angle of 15° with respect to a widthwise direction of the tire in thesame direction are formed in a central region rib at intervals of 30 mmin the circumferential direction over a full width of the rib and adepth of the sipe is 10 mm and an opening width thereof is 0.4 mm, andeach of the sipes is divided into three parts as shown in FIG. 8(b) andinclined at an angle of ±22.5° with respect to a radial direction of thetire in a depth direction.

Example Tire 24

In a tread pattern shown in FIG. 35, a plurality of ellipsoidal recessesinclined in the circumferential direction are formed in a central regionrib at intervals of 30 mm in the circumferential direction, and a lengthof a major axis of the recess is 13 mm and an inclination angle of themajor axis with respect to the widthwise direction of the tire is 15°and a length of a minor axis thereof is 3 mm.

Table 6 TABLE 6 Steering Resistance to Center FIG. stabilityhydroplaning wear Comparative 100 100 100 Example tire 9 Example 105 108105 tire 23 Example 102 108 104 tire 24

EXAMPLE 6

With respect to each of example tire and comparative example tireshaving a tire size of 205/66 R15, the conicity force on a tire-wheelassembly is measured and the steering stability and resistance tohydroplaning are measured to obtain results as shown in Table 7.

In this table, Example tire 25 has a tread pattern shown in FIG. 12,wherein circumferential main grooves having a depth of 8 mm areasymmetrically arranged in axially inner side and outer side to bemounted, and a ratio of effective ground contact area S_(out) at theaxially outer side to ground contact area S_(in) at the axially innerside bordering the equatorial line E of the tire is 1.14, and a radialdistance from a tangential line T on an outer side surface of the treadat a position corresponding to 80% of a tread width W is 5.8 mm at theaxially outer side and 6.2 mm at the axially inner side.

Comparative Example tire 10 has a symmetrical tread pattern shown inFIG. 37, wherein circumferential main grooves having a depth of 8 mm aresymmetrically arranged with respect to the equatorial line of the tireto substantially equalize the effective ground contact area at theaxially inner side and axially outer side, and the radial distance froma tangential line T on an outer side surface of the tread at a positioncorresponding to 80% of a tread width W is made substantially equal atthe axially inner side and axially outer side.

The steering stability is evaluated by feeling in the running on a testcircuit course, and the resistance to hydroplaning is evaluated byfeeling in the running on a straight road surface having a water depthof 6 mm. Moreover, the larger the index value in the table as to theseperformances, the better the result.

Also, the conicity force is determined by an average of found values on10 tires of each example.

Table 7 TABLE 7 Steering Resistance to Conicity force FIG. stabilityhydroplaning (N) Example tire 25 105 108 20 Comparative 100 100 18Example tire 10 Comparative 108 108 86 Example tire 11

As seen from Table 7, the example tire produces high steering stabilityand resistance to hydroplaning and can control the conicity force to thesame extend as in the symmetrical pattern of Comparative example tire10.

INDUSTRIAL APPLICABILITY OF THE INVENTION

As seen from the above, according to the invention, the resistance tohydroplaning and steering stability are improved and the noise in therotation of the tire can be advantageously reduced without lowering theresistance to uneven wear.

1. A pneumatic tire comprising three or more circumferential maingrooves asymmetrically positioned with respect to an equatorial line ofthe tire and extending linearly and continuously in the circumferentialdirection of the tread formed in a ground contact face of the tread toform one or more land part rows in each of the resulting central regionand both side regions, in which a sum of groove volume in acircumferential direction in lateral grooves formed in a shoulder landpart row corresponding to an axially inner side of the tire mounted on avehicle per unit width is made smaller than a sum of groove volume inthe circumferential direction in lateral grooves formed in a shoulderland part row corresponding to an axially outer side of the tire mountedon the vehicle, and the land part row in the central region is renderedinto a rib, and a plurality of slant grooves extending at an averageinclination angle of not less than 45° with respect to a widthwisedirection of the tread are arranged in a second inner land part rowlocated at a side of the equatorial line adjacent to a shoulder landpart row at the axially inner side and these slant grooves are opened tothe circumferential main groove at least located adjacent to the secondinner land part row of the axially inner side.
 2. A pneumatic tireaccording to claim 1, wherein the number of the circumferential maingrooves is 4 or more, and a plurality of lateral grooves opening ateither one end to the circumferential main groove and terminating at theother end in the land part row are formed in a second outer land partrow located adjacent to the side of the equatorial line of the tire inthe shoulder land part row of the axially outer side.
 3. A pneumatictire according to claim 1, wherein the shoulder land part row of theaxially inner side is divided into two parts by a fine groove extendingin a circumferential direction, and an average angle of the lateralgroove formed in the shoulder land part row of the axially outer sidewith respect to the widthwise direction of the tread is not more than15°.
 4. A pneumatic tire according to claim 1, wherein the shoulder landpart row of the axially inner side is divided into two parts by a finegroove extending in a circumferential direction, and one divided portionlocated at a side of a tread end is a narrow-width rib and a pluralityof small holes separated from the groove are formed in the otherwide-width divided portion, which may be provided with lateral grooves.5. A pneumatic tire according to claim 3, wherein a groove width of thefine groove is made wider in a side of a tread surface than in a groovebottom.
 6. A pneumatic tire according to claim 4, wherein a total volumeof plural small holes formed in the wide-width divided part at theshoulder land part row of the axially inner side in the circumferentialdirection of the tread is made larger at a side of the fine groove thanat a side of the equatorial line of the tire.
 7. A pneumatic tireaccording to claim 4, wherein the wide-width divided portion havingsmall holes a tread structure contacting with ground in at least a partof small hole forming region at a posture of applying a camber angle of−0.5° under an action of a load corresponding to 40% of a maximum loadcapacity.
 8. A pneumatic tire according to claim 4, wherein a side wallof the narrow-width rib located at a side of a tread end is a curvedform having at least one center of curvature at an outer side of a crosssectional profile line.
 9. A pneumatic tire according to claim 1,wherein a center line of a rib of the central region land part rowlocated nearest to the side of the equatorial line of the tire is biasedto the axially inner side with respect to the equatorial line of thetire, and a plurality of widthwise fine grooves extending obliquely withrespect to the widthwise direction of the tread are formed in this rib.10. A pneumatic tire according to claim 9, wherein an inclination angleof the widthwise fine groove is an average angle within a range of5-55°.
 11. A pneumatic tire according to claim 9, wherein the widthwisefine groove is formed so as to incline in a depth direction in form of acurved face provided that it is separated away from each other borderinga middle part of its extending direction.
 12. A pneumatic tire accordingto claim 9, wherein at least a part of the widthwise fine grooves isterminated at both ends in the rib.
 13. A pneumatic tire according toclaim 1, wherein a center line of a rib of the central region land partrow located nearest to the side of the equatorial line of the tire isbiased to the axially inner side with respect to the equatorial line ofthe tire, and a plurality of recesses having substantially anellipsoidal form are formed in this rib, and a major axis of each of therecesses is extended at an angle of 5-45° with respect to the widthwisedirection of the tread, and a side of the shoulder land part row in therib at the axially inner side is defined by the circumferential maingroove extending linearly.
 14. A pneumatic tire according to claim 13,wherein at least a part of the recesses is provided with a sipe(s)extending in a direction of the major axis.
 15. A pneumatic tireaccording to claim 1, wherein the rib of the central region land partrow located nearest to the equatorial line of the tire is defined by apair of circumferential main grooves extending linearly, and a groovewidth of the circumferential main groove located at a side of theshoulder land part row of the axially inner side is made wider than agroove width of the circumferential main groove located at a side of theshoulder land part row of the axially outer side.
 16. A pneumatic tireaccording to claim 1, wherein a peripheral upheaved portion graduallydecreasing a surface height toward at least one of a side edge of ablock and a central region of a block is formed in each of blocksdefined by the lateral grooves in the shoulder land part row of theaxially outer side.
 17. A pneumatic tire according to claim 1, wherein aheight of a leading edge and a height of a trailing edge in a blockdefined by the slant grooves in at least a second inner land part roware made different in the widthwise direction of the tread, and each ofhigh height portions is extended in the circumferential direction of thetread while changing positions in the widthwise direction of the treadin accordance with positions in the circumferential direction.
 18. Apneumatic tire according to claim 1, wherein a slant face graduallydecreasing a height toward a top is formed in an acute corner portion ofa block defined by at least one of the lateral groove and the slantgroove extending at an average angle of not less than 45° with respectto the widthwise direction of the tread.
 19. A pneumatic tire accordingto claim 1, wherein a projection part projecting into a groove isdisposed in a groove wall of the circumferential main groove opposite toa groove wall opening to at least one of the lateral groove and theslant groove at a groove opening position and a position opposite to thewidthwise direction of the tread.
 20. A pneumatic tire according toclaim 1, wherein a groove depth of the slant groove extending at anaverage angle of not less than 45° with respect to the widthwisedirection of the tread is deepened from the side of the equatorial lineof the tire toward the side of the tread end.
 21. A pneumatic tireaccording to claim 1, wherein extending directions of the slant groovesformed in the second inner land part row with respect to the widthwisedirection are alternately rendered into opposite directions in thecircumferential direction of the tread.
 22. A pneumatic tire accordingto claim 1, wherein an integral value of the rigidity in the widthwisedirection of the tread over a full ground contact length in each of theland part rows defined by the circumferential main grooves is within arange of 50% from a large value between mutually adjacent land partrows.
 23. A pneumatic tire according to claim 1, wherein at a state thatthe tire is mounted onto an approved rim and inflated under a normal airpressure and loaded under a mass corresponding to the maximum loadcapacity, an effective ground contact area at either axially inner sideor axially outer side is larger than that at the remaining other side,and a radial distance from a tangential line on the outer side surfaceof the tread perpendicular to the equatorial plane of the tire up to theground contact edge of the tread at a posture of filling the normal airpressure is made larger at the mounting side having a small effectiveground contact area than at the other mounting side.
 24. A pneumatictire according to claim 23, wherein a relation between a ratio of smalland large effective ground contact areas (S-large/S-small) and a ratioof large and small radial distance (H-large/H-small) satisfiesS-large/S-small=A×(H-large/H-small) wherein A is 1.0-1.4.
 25. Atire-wheel assembly formed by assembling a pneumatic tire as claimed inclaim 1 onto a wheel, in which a connecting portion between a rim and adisc of the wheel is located toward an outer side of a vehicle to bemounted with respect to the equatorial plane of the tire.